Process of recovering sulphuric acid from spent sulphuric acid



C. L. READ 'Dec. 8, 1942.

PROCESS OF RECOVERING SULPHURIC ACID FROM SPENT SULPHURC ACID FiledMarch 14, 1940 .0N T3525 NN lll" NN NN wml www Frhll in the acidregeneration cycle.

Patented Dec. 8, 1942 PRDCESS OF RECOVERING SULPHURIC ACID FROM SPENTSULPHURIC ACID' Chester L. Read, Westfield, N. J., assigner to StandardOil Development Company, a corporation of Delaware Application March 14,1940, Serial No. 323,854

v8 Claims. (Cl. 23-173) The-present invention relates to the refining ofmineral oils. The invention is especially concerned with the recovery ofmineral acids used in the refining of petroleum oils. In accordance withthe present process, spent acids secured in the refining of mineral oilsand in the manufacture of intermediate products such as alcohols,esters, and ethers from olefns are re-extracted in an eiiicient andeconomical process in a manner whereby increased yields of high qualityregenerated acids are secured. The process essentially comprises atwo-stage operation in which the spent acid secured from theseoperations is treated in an initial stage with a primary solvent of thecharacter of phenol and further treated in a secondary stage with asecondary mineral oil solvent. The acid after removal from the mineraloil is reconcentrated in any desirable manner and recycled to thesystem.

It is well known in the art to refine mineral oils, utilizing variousinorganic acids. For example, it is known to remove sulphur compoundsand various other deleterious substances from petroleum fractions,particularly those fractions boiling in the motor fuel boiling range, bytreating the same with sulphuric acids of various concentrations. It isalso known to produce various products, as for example, alcohols,

esters, and ethers from olens utilizing sulphuric acid as a reagent.'Ihese processes are commercially justied to a large extent upon theeiiiciency and the cost of regenerating the various reagents,particularly the sulphuric acid. Thus, suggestions have been made thatspent acids secured in the processing of mineral oils be hydrolyzed andtreated with a selective solvent of the class which have a preferentialselectivity for the relatively more aromatic constituents as compared tothe relatively more paramnic constituents as for example phenols,beta-beta-dichlor-diethyl ether and nitro benzene prior to concentratingthe vacid by the application of heat or other means. Processes of thischaracter represent distinct improvements Suitable selective solventsfor extracting the spent acid are quite expensive and every effort isexerted to avoid loss of the same. However, loss of solvent has not beenentirely prevented in processes of this character-due to the fact thatan appreciable quantity is soluble in the acid liquor, is thus removedw'lth the same and lost when the acid is re-concentrated by theapplication of heat. I have now discovered an improved process bycompletely eliminated. The process of my in which spent acids may beeconomically processed for the productionl of high quality acids whichmay be readily recycled tothe system and in which loss of valuablereagent is substantially vention maybe readily understood by referenceto theattached drawing illustrating modications of the same. Feed oil,which for the purposes of illustration is taken to be a petroleum oilboiling in the motor fuel boiling range, is introduced into acidtreating plant I by means of feed line 2, wherein it is contacted withsulphuric acid which is introduced'. by means of feed line 3. Thetreated oil is removed from acid treating plant I byfmeans of line 4,while the acid vsludge is removed by means of line 5. The acid sludgecontaining tarry hydrocarbon materials is then hydrolyzed with waterwhich is introduced by means of line 6. The mixture is then passedthrough mixer 'I and into settler or equivalent means 8. Theprecipitatedv tarryhydrocarbon materials are withdrawn from settlingunit 8 by means of line 9, while the hydrolyzed spent acid is withdrawnby means of line I0 and introduced into acidV storage 'II. The spentweak acid is withdrawn from storage II by means of line I2, and passedto solvent treating plant I3, which for the purposes oi description istaken to be a countercurrent solvent treating tower. The spent acidflows downwardly through tower I3 and contacts an upflowing solvent ofthe character of phenol as for example cresol, which is introduced intosolvent treating tower I3 by means of line I4. Temperature and pressureconditions are adapted to secure the formation of a solventV phase whichis withdrawn from tower I3 by means of line I5 and an acid phasesubstantially free of oily materials which is withdrawn-by lmeans ofline I6.

The solvent phase may be passed through heating zone 30 and is thenintroduced into solvent recovery tower I8 by means of line I9.Temperature and pressure. conditions are adjusted in tower I8 adapted toremove ,overhead substantially purephenol by means of line 20 and toremove as a bottoms a solvent-free extract oil by means of line 2 I. Thesolvent removed overhead from solvent recovery tower I8 by means of line20 is passed to solvent storage 2| from which it is preferably recycledto solvent treating tower I3. The acid phase withdrawn from tower I3 bymeans of line I6 containing dissolved therein an appreciable amount ofthe cresol is then passed to secondary extraction unit I1, wherein it iscontacted with a secondary non-reactive petroleum oil solvent which isintroduced by means of line 31|. illustration it is assumed thatcontacting, plant l1 comprises a countercurrent solvent treating tower.y Temperature and pressure conditions are adapted to remove by means ofline 32 a secondary oil solvent and cresol phase substantially free ofacid and to remove by means of line 33 an acid phase substantially freeof secondary oil solvent and cresol. This latter phase is passed toregeneration plant 34 which may comprise any desirable number andarrangement of stages in which the acid is concentrated to the desiredextent by the removal of water. The regenerated acid is withdrawn fromregeneration plant 34 by means of line 3 and recycled to acid treatingplant I. The secondary oil solvent phase withdrawn by means of line 32is passed to heating zone 22 and introduced into distillation unit 23.Temperature and pressure conditions are adapted to remove overhead fromunit 23 by means of line 24 the phenolic solvent which is passed tostorage 2l. The secondary petroleum oil solvent is withdrawn from unit23 by means of line 25 and passed to secondary solvent storage 26 fromwhich it is recycled to extraction zone l1 by means of line I8.

The process of the present invention may be widely varied. The inventionmay be readily adapted to the' recovery utilized in the -regeneration ofspent acids secured in various refining and related operations. 'I'heprocess, however, is particularly applicable in the recovery of phenolutilized in the regeneration of spent acids secured in the refining ofpetroleum oils boiling in the motor fuel boiling range. Although thepresent process may be adapted under certain conditions for thetreatment of acids of any concentration particularly desirable resultsare secured providing the spent acid be diluted to a concentration offrom 30% to 60% preferably to about 40% to 50% prior to extracting thesame with a phenol. The preferred concentration will vary to some extentsince as the molecular weight of the monophenols is increased thesolubility in weak sulphuric acid solutions is decreased. Methyl phenol,for example, is 50% as soluble as monohydroxy phenol.

For purposes of The solubilities of the high molecular weight' phenolsare low but as the molecular weight increases the boiling point likewiseincreases and the diillculty of recovering the solvent from the extractoil is similarly increased.

Although in general solvents selected from the class of solvents whichhave a preferential selectivity' for the relative more aromaticconstituents of a petroleum oil as-compared to the relative moreparaiinic constituents may be used for extracting the spent acid as forexample nitro benzene and beta-beta-dichlor-diethyl ether it ispreferable to employ phenolic type solvent. The amount of the phenolictype primary solvent employed to extract the spent acid may varyconsiderably, depending the acid and the character of the impuritiesdisvolved therein. In general, when treating sulphuric acid having aconcentration in the range from about 30% to 60% with a phenol it ispreferred to use from 0.1 to 1.0 volume preferably from 0.4 to 0.6volume of a phenol per volume of spent acid. The temperature andpressure conditions likewise may vary. considerable, depending uponoperating conditions. In general, it is preferred to employ atmospherictemperatures and pressures. i

The secondary solvent utilized comprises a peupon the concentration of.

of phenolic type solvents derived from a troleum oil which issubstantially non-reactive with the spent acid. The secondary solvent ispreferably a highly paraillnic petroleum oil fraction having a gravityin the range from about 25 A. 1 I. to 35 A. P. I. It is likewisepreferred that the bcling range be from about 500 F. to l700v F. Anyhighly parafiinic petroleum oil having an initial boiling point of about50 F. or more above the boiling range of the primary solvent however maybe used. The quantity of secondary solvent employed will depend upon theparticular primary solvent used, as well as upon other operatingconditions. In general, it is pre- ExAurLl: 1

Various tests were made to determine the solubility of methyl phenolandphenol in sulphuric acid of varying concentrations. The results of thesetests are as follows:

Solubility of phenol and cresol in H2304 at +75 F.

cr'eml solubility Phenol solubility Acid coic.

perce Percent by Percent of Percent b y Percent of Wt. H1304 Wt. H28043. 2 8. 5 l. 6 0. 5 l. 9 0. 8 3. 1 0. 45 l. l5 1. 0 2. 4 0. 8 l. 25 l.85 2. 9

(l) (1) (l) (l) l Miscble Exmu 2 A spent sulphuric acid secured in thetreatment of a petroleum naphtha boiling in the motor fuel boiling rangewas hydrolyzed to approximately 40% concentration. The spent acid had a5% carbon content. This acid was batch extracted with 50% of cresylicacid which produced an acid product having 0.2% carbon and 0.5% ofcresylic acid dissolved in the sulphuric acid. The cresylic acid wassubstantially ccmpletely recovered from the acid by extracting the samewith a petroleum oil secondary solvent Mid-Continent lube distillate.The secondary solvent had a Saybolt viscosity at 210 of 60 and a 450ash. The results of these operations were as followsz Percent ofcresylic acid Percent oi secondary solvent based on weak acid solutionrecovered The process of the present invention is noty to be limited byany theory or mode of operation, but only in and by the following claimsin which it is desired to claim all novelty in so far as the prior artpermits.

I claim:

l. Process for the regeneration of a spent sulphuric acid secured frompetroleum oil refining operations comprising hydrolyzing said spent acidand then countercurrently contacting the same with a primary phenolsolvent under conditions to form a solvent phase and an acid phasecontaining an appreciable amountof the primary solvent, countercurrentlycontacting said acid phase with a highly paraftinic oil fraction havinga gravity in the range of about 25 A. P. I. to 35 A. P. I. underconditions to form a highly parainic oil phase containing dissolvedtherein said appreciable amount of primary solventv and an acid phase,reconcentrating said acid and separating said appreciable amount of theprimary solvent from the highly parailinic oil fraction.

, 2. Process in accordance with claim 1 in which said spent acid ishydrolyzed to an acid concentration of from 30% to 60%.

3. Process in accordance with claim 1 in which said spent acid ishydrolyzed to about 40% to 50% acid concentration and said primarysolvent is cresol.

4. Process in accordance with claim 1 in which said spent acid iscontacted with from 0.4 volume to 0.6 volume of primary solvent pervolume of spent acid and in which said acid phase derived from theinitial extraction is contacted with from 0.4 volume to 0.6 volume of ahighly parafflnic petroleum oil fraction having a gravity in the rangefrom about 25 A. P. I. to 35 A. P. I. per'volume of acid phase.

5. Process in accordance with claim 1 in which said primary solvent iscresol.

6. Process in accordance with claim 1 in which said primary solvent iscresol and in which from about 0.4 volume to 0.6 volume of phenol andhighly paraflnic petroleum oil are employed per volume of feed to therespective extraction stages.

the class consisting of phenols, nitrobenzene, and beta-beta-dichiordiethyl ether under Iconditions to form a primary solvent extract phasecontaining said carbonaceous constituents and a spent acid phasecontaining an appreciable amount of said primary solvent, separating thespent acid phase from the primary solvent extract phase yand contactingsaid -spent acid phase with a highly parailnc petroleum oil solventhaving a gravity in the range from about A. P. I. to about 35 A. P. I.under conditions substantially completely to remove this primary solventfrom said spent acid and to form a highly paraflinic petroleum oilphas'e containing dissolved therein said primary solvent and la spentacid phase, separating the respective phases, regenerating said spentacid phase and recovering said primary solvent from said highly paralnicpetroleum oil. v

8. Process for the regeneration of a spent sul'- phuric acid containingdissolved carbonaceous constituents secured in the treatment ofpetrovleum oils comprising contacting a spent sul- 7. Process for theregeneration of a spent sul- I phuric acid containing dissolvedcarbonaceous `constituents secured in the treatment of petroleum oilscomprising contacting a spent sulphuric acid with a primary solventselected from phuric acid with phenol under conditions to form a phenolphase containing said carbonaceous constituents and a spent acid phasecontaining an appreciable amount of said phenol, separating the spentacid phase from the phenol phase and contacting the spent acid paramnicpetroleumoil fraction having a gravity in the range from about 25 A. P.Lto about 35 A. P. I. under conditions to substantially completelyremove said phenol from said spent acid phase and to form a highlyparalnic petroleum oil phase containing dissolved therein said phenoland a spent acid phase, -separating the re spective phases, regeneratingsaid spent acid phase and recovering said phenol from said highlyparafnic petroleum oil.

CHESTER. L. READ.

phase with a highly

